Lake Cerknica is one of the largest intermittent lakes in Europe. It appears every year on the karst polje (plain), caught between the Javorniki hills and the Bloke plateau on one side, and Mount Slivnica on the other, 20 km from Postojna town. During the dry season, the lake disappears, which enables paddling, fishing, hiking or grass mowing in the same area in just one year. The lake normally stays on the Cerknica plain for about eight months a year. Water usually spreads over the surface of 20 km2, but at its fullest, the lake covers a surface of nearly 30 km2. When full, Lake Cerknica becomes the largest lake in Slovenia.
It was first mentioned as early as ancient history, and it has been included on the maps of Europe ever since the 15th century. The hydrology of the lake was first researched by Carniolan natural historian Johann Weikhard von Valvasor, which won him a Fellowship of the Royal Society. Here is the cradle of karstology and terms such as karst polje (plain) and intermittent lake. The importance of intermittent Lake Cerknica, therefore, goes far beyond Slovenia’s borders. Along with the Rakov Škocjan valley and the Križna jama cave, Lake Cerknica has been designated as a wetland of international importance – Ramsar Site, and also as a Natura 2000 Site because of its importance for the preservation of endangered birds.
In the area, 276 bird species have been observed – one half of all European species; this is home to 45 mammal species – one half of all European species; 125 butterfly species can be spotted here – a little less than a third of all European species; 15 amphibian species spawn by the lake – nearly a quarter of all European amphibians… Biodiversity of the region is truly exceptional! People from across the region have strong ties to intermittent Lake Cerknica as well. The abundance of fish and game has attracted people and provided them with nourishment since the Stone Age. After all, generations of hard-working hands have co-shaped the typical landscape on the moist soil of the basin, and by maintaining the flood meadows, they continue to ensure habitat for endangered flora and fauna.
Intermittent Lake Cerknica acts a strong magnet to birds. So far, more than half of all European bird species have been observed in this area. The ever-changing landscape creates unique opportunities to observe these animals in their everyday activities throughout the year. Fish have attracted people to the shore, ponors and sinkholes of Lake Cerknica since prehistoric time, but beasts and flocks of birds feasted by the drained lake long before the first humans. Lake Cerknica is home to the tiniest snail, the biggest of bears, and everything in between. The diverse flora and fauna of the area have always captivated natural scientists and nature enthusiasts, and they always offer something new, yet unseen…
Are there plants which ‘eat’ animals? Yes, there are. Intermittent Lake Cerknica is home to three species of carnivorous plants: intermediate bladderwort, bladderwort and oblong-leaved sundew. Visitors are instantly charmed by wet meadows rich with endangered and protected plants. Wild gladioli and orchids (early marsh orchid, broad-leaved marsh orchid, marsh orchid and marsh helleborine) thrive here in such numbers that one may doubt they are endangered. Among the most obvious species with colourful flowers found in the area of Lake Cerknica, there are also tens of grass-like endangered species. They may not be eye-catching, but many of them form typical communities and are, therefore, of great importance for the intermittent lake’s ecosystem.